1. Field of the Invention
The present invention relates to a piezoelectric actuator, a liquid transporting apparatus, and a method for producing a piezoelectric actuator.
2. Description of the Related Art
An example of a liquid-transporting apparatus which transport a liquid is an ink-jet head which discharges ink from its nozzles to perform printing. Such an ink-jet head includes a piezoelectric actuator which applies pressure to ink. This piezoelectric actuator can be exemplified by a piezoelectric actuator which has a plurality of stacked piezoelectric layers and two kinds of plurality of inner electrodes arranged alternately between the piezoelectric layers. Such a piezoelectric actuator is constructed, for example, such that the inner electrodes of one kind are conducted with each other, and the inner electrodes of the other kind are conducted with each other; both kinds of inner electrodes are connected to a drive circuit which applies a drive voltage; and that difference in the electric potential between the two kinds of inner electrodes are generated to deform the piezoelectric layers at portions each of which is sandwiched between an inner electrode of one kind and an inner electrode of the other kind, thereby applying pressure to the ink.
For example, a piezoelectric actuator for an ink-jet head, shown in FIG. 1 of Japanese Patent Application Laid-open No. 2004-358716, has a plurality of piezoelectric elements corresponding to a plurality of nozzles respectively, and each of the piezoelectric elements has a plurality of stacked piezoelectric layers and two kinds of plurality of inner electrodes, in which inner electrodes of one kind and inner electrodes of the other kind are arranged alternately between the stacked piezoelectric layers. In this piezoelectric actuator, the inner electrodes of one kind, which are arranged alternately with the inner electrodes of the other kind intervening therebetween, are conducted with each other via an external electrode formed in one side surface of each of the piezoelectric elements, and the inner electrodes of the other kind, which are arranged alternately with the inner electrodes of one kind intervening therebetween, are conducted with each other via an external electrode formed in the other side surface of each of the piezoelectric elements. Further, the external electrodes on both side surfaces respectively are connected to a drive circuit by a flexible flat cable (FFC). Namely, the piezoelectric actuator is constructed such that a predetermined voltage is applied via the FFC to the inner electrodes of a same kind, which are arranged alternately.
On the other hand, ink-jet heads described in U.S. Pat. No. 6,604,817 (corresponding to Japanese Patent Application Laid-open No. 2001-260349), U.S. Pat. No. 6,631,981 (corresponding to Japanese Patent Application Laid-open No. 2002-19102), and U.S. Pat. No. 4,766,671 (corresponding to Japanese Publication after Examination No. 7-96301) each include piezoelectric elements covering a plurality of pressure chambers respectively. Each of the piezoelectric elements has stacked piezoelectric layers and two kinds of electrodes arranged alternately between the piezoelectric layers, in which electrodes of a same kind are conducted with each other via a conductive material filled in a through hole or groove formed in the piezoelectric layers. In each case, a plurality of terminals (electrodes) connected to the conductive material is formed on a surface of the piezoelectric layer on the side opposite to the pressure chambers, and the electrodes are connected to a drive circuit via these terminals respectively.
However, for connecting a terminal of FFC to each of the outer terminals formed on the side surfaces of each of the piezoelectric elements, a complex structure for electric connection is required. In particular, when the piezoelectric elements are arranged highly densely to perform a high-quality printing, the connection becomes more difficult, which lowers the reliability of electric connection, or increases the cost of production. There is also a fear that the connection between the FFC and the outer electrodes arranged in the side surfaces of piezoelectric element is broken or disconnected when the piezoelectric element is deformed, consequently lowering the reliability of ink-jet head.
Further, in the ink-jet heads, described U.S. Pat. Nos. 6,604,817, 6,631,981, and 4,766,671 respectively, a surface of the piezoelectric layer on the side of pressure chambers is exposed to the pressure chambers. Accordingly, upon forming through holes connecting the electrodes, the location and/or depth of through holes must be carefully determined to prevent the through holes from communicating with the pressure chambers. Further, in the ink-jet head described in each of these U.S. patents, the piezoelectric layer is formed continuously across a plurality of pressure chambers. Therefore, when a certain portion of the piezoelectric layer facing a certain pressure chamber is deformed to apply pressure to the certain pressure chamber, there arises a problem of so-called cross talk in which the deformation of the certain portion of the piezoelectric layer is propagated to another portion of the piezoelectric layer corresponding to a pressure chamber adjacent to the certain pressure chamber. In addition, terminals (electrodes) each connected to a conductive material are formed on a surface of the piezoelectric layer on a side opposite to the pressure chambers to connect these terminals to an external wiring member such as FFC. Since the connection with the external wiring member such as FFC is very weak against external force, the reliability of connection of these terminals to the FFC also becomes a problem in some cases.